[Bug 1867375] Re: systemd-networkd: UseRoutes behavior change with introduction of UseGateway param

[Dan Streetman]

** Description changed:

- requesting backport of PR https://github.com/systemd/systemd/pull/14983 which fixes the issue described in 
+ [impact]
+ 
+ the networkd UseRoutes parameter allowed ignoring all routes provided by
+ a dhcp4 server, including the route via the dhcp4-provided gateway.
+ This was the behavior of networkd until recently, and in Focal the
+ UseRoutes parameter does *not* prevent networkd from adding the route
+ via the dhcp4-provided gateway.  This is now controlled with a new
+ parameter, UseGateway.
+ 
+ The systemd in Focal unfortunately has part of the upstream code; it no
+ longer ignores the gateway route when UseRoutes=false is specified, but
+ also it does not include the UseGateway parameter.
+ 
+ [test case]
+ 
+ bug 1872589 has a good test case netplan config, but a very quick test
+ can be done with the networkd config:
+ 
+ [Match]
+ Name=eth0
+ 
+ [Network]
+ DHCP=ipv4
+ LinkLocalAddressing=ipv6
+ 
+ [DHCP]
+ RouteMetric=100
+ UseMTU=true
+ UseRoutes=false
+ 
+ 
+ this results in the system incorrectly setting a route via the default gateway:
+ 
+ root at lp1867375-f:~# ip r
+ default via 10.202.51.1 dev eth0 proto dhcp src 10.202.51.86 metric 100 
+ 10.202.51.0/24 dev eth0 proto kernel scope link src 10.202.51.86 
+ 10.202.51.1 dev eth0 proto dhcp scope link src 10.202.51.86 metric 100 
+ 
+ [regression potential]
+ 
+ tbd
+ 
+ [other info]
+ 
+ to properly support separation of 'routes' and 'gateways' received via
+ dhcp4, SRU releases should also support the UseGateway parameter, which
+ is what this bug was originally opened requesting.
+ 
+ [original description]
+ 
+ requesting backport of PR https://github.com/systemd/systemd/pull/14983 which fixes the issue described in
  https://github.com/systemd/systemd/issues/14982 to 18.04 (bionic)

** Also affects: systemd (Ubuntu Focal)
   Importance: Undecided
       Status: Fix Released

** Also affects: netplan.io (Ubuntu Focal)
   Importance: Undecided
       Status: New

** Changed in: netplan.io (Ubuntu Bionic)
       Status: New => Invalid

** Changed in: netplan.io (Ubuntu Eoan)
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/1867375

Title:
  systemd-networkd: UseRoutes behavior change with introduction of
  UseGateway param

Status in netplan.io package in Ubuntu:
  New
Status in systemd package in Ubuntu:
  Fix Released
Status in netplan.io source package in Bionic:
  Invalid
Status in systemd source package in Bionic:
  Confirmed
Status in netplan.io source package in Eoan:
  Invalid
Status in systemd source package in Eoan:
  Confirmed
Status in netplan.io source package in Focal:
  New
Status in systemd source package in Focal:
  Fix Released

Bug description:
  [impact]

  the networkd UseRoutes parameter allowed ignoring all routes provided
  by a dhcp4 server, including the route via the dhcp4-provided gateway.
  This was the behavior of networkd until recently, and in Focal the
  UseRoutes parameter does *not* prevent networkd from adding the route
  via the dhcp4-provided gateway.  This is now controlled with a new
  parameter, UseGateway.

  The systemd in Focal unfortunately has part of the upstream code; it
  no longer ignores the gateway route when UseRoutes=false is specified,
  but also it does not include the UseGateway parameter.

  [test case]

  bug 1872589 has a good test case netplan config, but a very quick test
  can be done with the networkd config:

  [Match]
  Name=eth0

  [Network]
  DHCP=ipv4
  LinkLocalAddressing=ipv6

  [DHCP]
  RouteMetric=100
  UseMTU=true
  UseRoutes=false

  
  this results in the system incorrectly setting a route via the default gateway:

  root at lp1867375-f:~# ip r
  default via 10.202.51.1 dev eth0 proto dhcp src 10.202.51.86 metric 100 
  10.202.51.0/24 dev eth0 proto kernel scope link src 10.202.51.86 
  10.202.51.1 dev eth0 proto dhcp scope link src 10.202.51.86 metric 100 

  [regression potential]

  tbd

  [other info]

  to properly support separation of 'routes' and 'gateways' received via
  dhcp4, SRU releases should also support the UseGateway parameter,
  which is what this bug was originally opened requesting.

  [original description]

  requesting backport of PR https://github.com/systemd/systemd/pull/14983 which fixes the issue described in
  https://github.com/systemd/systemd/issues/14982 to 18.04 (bionic)

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